The proper alignment of a head in a magnetic storage device (e.g., tape drive apparatus or hard disk apparatus) is extremely critical. Thus, for optimum performance in a tape drive apparatus the tape must be in intimate contact with the head and accurately aligned to it. In a magnetic disk storage device, the head must also be properly aligned and mounted relative to the magnetic disk.
In a tape drive apparatus the most important alignment parameters which must be controlled are those which influence azimuth angle, tape flying height (distance between the tape and the head), and off-track error. The azimuth angle (head-gap to tape-path angle) affects phase distortion and signal amplitude. The tape flying height is a function of tape tension, tape wrap angle, head penetration, yaw, zenith and head geometry. Off-track error (head gap position relative to the written track) can introduce erroneous data sensing (e.g., from adjacent tracks).
Some of these parameters may be controlled by factors such as head design, head actuation system, and cartridge referencing (e.g., in a tape drive apparatus). However, the alignment and mounting of the head are extremely critical.
The position of the head is determined by three linear dimensions (penetration, offset, and off-track) and by three angular dimensions (azimuth, yaw, and zenith). The accuracy of placement of the head in each of these dimensions controls the performance of the head.
One manner of aligning and mounting a magnetic head in a magnetic storage device is to temporarily fasten the head to a carrier or support in the device itself and then align the head to the desired position optically. Such technique requires the use of a microscope (at least 500.times. to 1000.times.) in order to see the head gap (i.e., the gap between the two halves of the magnetic core for a read head, write head, or a read/write head). Special tooling is required to support the apparatus in a designated plane. Then, using the microscope, it is necessary to visually align the head gap to a position which is believed to be perpendicular to the designated plane.
This is a very time-consuming procedure, and each head must be individually aligned. Operator fatigue and operator error are variables which can easily affect the alignment accuracy. Also, the image quality of the microscope may be very poor, thereby introducing another source of error. This procedure also requires micro-manipulation or adjustment of the head in order to obtain proper alignment. The high cost of the tooling and the other required equipment (including high power microscope) is another disadvantage of this technique. Adjustments in the tooling may also be required in order to maintain accuracy in alignment.
Another manner of aligning a magnetic head in a magnetic storage device involves initially pre-mounting the head in a manner such that it can be moved slightly in order to align the azimuth prior to permanent mounting. Then the head is magnetically aligned using a specially prepared magnetic media (e.g., a tape, floppy disk, etc.) which has the flux transitions recorded at predetermined azimuth errors in a manner such that the amplitude of the signals read by an azimuth aligned head correspond with a predetermined pattern. One disadvantage of this technique is that it requires use of a specially prepared magnetic media which is expensive. Also, some of the allowable tolerance is already lost due to errors in the recording of the media itself. Furthermore, each head must be individually aligned. This technique also requires micro-manipulation or adjustment of the head during alignment.
Another manner of aligning and mounting a magnetic head (of the type having at least a pair of gaps on the same gap plane) in a magnetic storage device such as a tape drive apparatus involves the use of a precision fixture which simulates a tape cartridge or cassette. The head is aligned and clamped to the fixture. Then the fixture is inserted into the tape drive apparatus which clamps and references the fixture to the drive mechanism. This procedure fixes five of the degrees of freedom (all but the azimuth). The head is then tacked with adhesive to a bracket, which in turn is held to the tape drive by a small removable clamp. The preliminary fixture simulating a tape cartridge is then removed and the head is ready for azimuth adjustment. The small removable clamp holds the head and bracket assembly against the head carrier but it allows rotation of the head so as to enable adjustment of the azimuth angle.
A special tape cartridge can then be inserted into the drive, the cartridge being preformatted with keys written across the width of the tape and spaced a certain distance apart. By reading the keys with one vertical pair of in-line gaps (one read gap and one write gap) the time delay between the arrival of a key at each gap can be measured. The azimuth angle can then be calculated. Then the head can be rotated relative to the head carrier until the proper azimuth is obtained. At that time the head may be permanently fastened in place (e.g., with adhesive) on the carrier.
There are several disadvantages associated with the foregoing technique. For example, it may only be used when there are two or more gaps in the same plane. Specially prepared magnetic media is required. Some of the allowable tolerance is lost due to errors in the manufacture of the special magnetic media. Each head must also be individually aligned, and micro-adjustment is required. This also is a time-consuming technique, and special equipment is required.
Yet another technique for aligning a magnetic head involves a reference surface transfer. In this technique it is necessary to grind an external surface of the magnetic head to form a surface which is either perpendicular to the gap surface or parallel to the gap surface. The surface which has been so ground is then used as a reference surface to determine alignment of the head. One disadvantage of this technique is that the magnetic head becomes more costly because of the precision grinding required. Also, some tolerance is lost due to the grinding process. This technique may be used as the preliminary mounting procedure when using any of the other foregoing techniques when tight tolerance is required.